As a method for imparting oxygen gas barrier properties to a film, a sheet, or a molded body such as a bottle or a cup, which is made of a plastic, a technology of applying and drying an aqueous solution of a polyvinyl alcohol resin (hereinafter abbreviated as PVA resin) to form a PVA resin coated film or PVA resin layer, which is excellent in gas barrier properties, is useful.
However, since a PVA resin is a hydrophilic resin, it is poor in affinity to hydrophobic materials and, in the case where a substrate is a hydrophobic resin such as a polyolefin resin or a polyester resin, it is necessary to subject a surface of the substrate to a treatment with an anchoring agent or a hydrophilization treatment or to make an adhesive layer intervene. Of these, the surface treatment with an anchoring agent has widely been used but has problems that production steps increase and there is a possibility of exerting influence on properties.
Correspondingly, there has been proposed a multilayered film in which adhesiveness between the PVA resin layer and the substrate layer is improved by blending into a coating liquid containing an aqueous anchoring agent and a PVA resin to a polyolefin film substrate (see, for example, Patent Document 1).
On the other hand, for the purpose of improving printability, gas barrier properties, and transparency of a PVA laminated film, there has been proposed a laminated film in which a polyethyleneimine (hereinafter abbreviated as PEI) is blended in a small amount into a PVA layer (see, for example, Patent Document 2).